Cathode cylinder having a heater member supported by a plurality of flexible metal bands



Nov. 7, 1967 F. RICHTER 3,351,801

J. CATHODE CYLINDER HAVING A HEATER MEMBER SUPPORTED BY A PLURALITY OFFLEXIBLE METAL BANDS Filed Feb. 16, 1965 4 \[f a 1 i I 2 FIG. I 1

INVENTOR. JOHN E RICHTER United States Patent 3,351,801 CATHODE CYLINDERHAVING A HEATER MEM- BER SUPPORTED BY A PLURALITY 0F FLEXI- BLE METALBANDS John F. Richter, San Mateo, Calii'., assignor, by mesneassignments, to the United States of America as represented by theSecretary of the Navy Filed Feb. 16, 1965, Ser. No. 433,240 Claims. (Cl.313--270) This invention relates to electrontube cathode structure andmore particularly to such electron type cathode structure capable ofbeing rapidly heated to emission temperature.

Many power tube applications require high demand outputs at widelyspaced intervals. Overall efiiciency of such devices is degraded by theconstant power dissipation from the heater during the inter-pulse orstandby periods.

Consequently much power can be conserved if a tubes cathode can bebrought to operating temperature only at the times when the tube isrequired to produce an output, i.e., during standby periods the tubescathode is not heated. The chief problem in such an arrangement is inproviding a cathode which heats very rapidly and structural support forthe cathode which can endure the rapid thermal expansion during heatingperiods.

An object of the present invention is to provide an electron tube havinga high average efficiency.

Another object of the present invention is to provide an electron tubehaving a cathode which can be rapidly heated.

A further object of the present invention is to provide electron tubecathode structure capable of being rapidly brought to emissiontemperature and capable of enduring rapid thermal expansion.

The present invention attempts to solve the above problems and objectsby providing a cathode element having very low thermal mass and uniquesupport structure for the cathode which can endure repeated thermalexpansion and contraction.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a cross-section View of a cathode structure of the presentinvention;

FIG. 2 is a pictorial view of the cathode support structure of thepresent invention.

In FIG. 1 an electron tube 1 utilizing a cathode 2 is shown. Otherelements such as the grid and plate have been eliminated to more clearlyshow the cathode structure. Cylindrical cathode 2 is provided with acircular end plate 3 having a small hole in its center. Heater supportrod 4 passes through the small hole and is bonded to the plate 3 atpoint C. Hence one end of support rod 4 is rigidly attached to thecylindrical cathode. Heater coils 5 and 6 are brazed or otherwise bondedto rod 4 at point D. Terminal lead wires 7 and 8 are bonded to coils 5and 6 at points C and D respectively. Coil 5 is the primary heater coilused during normal operation of the tube whereas coil 6 is an auxiliaryheater for heating the cathode by radiation during conversion of thealkaline earth carbonates during evacuation of the tube. Leads 7 and 8are, of course, connected to the appropriate terminals on a base 14. Aplurality of pins 10 are fastened to sleeves 12 on bottom 11 of thecylindrical cathode and provide the lower support for the cathode andthe electrical connection thereto.

The bottom of rod 4 is flexibly attached to base 14 to allow formovement of the rod during heating and cooling. The flexible supportstructure is best seen in 3,351,801 Patented Nov. 7, 1967 FIG. 2. Thebottom of rod 4 is bonded to washer 15 at its center opening 16. Supportstraps 13 are then radially arranged in asymmetrical mannerwabout thewasher 15 and bonded thereto. Each strap is then twisted and attached tovertical support pins 9 which are fixed to the base 14 as shown. In theparticular embodiment three straps were used and provided gooddimensional stability and freedom 'for vertical movement.

When the cathode is heated it consequently expands. Since rod 4 isrigidly attachedto the cathode at point A it is subjected to somemovement during heating. The instant support structure permits rod 4 tomove along its vertical axis and thus follow any expansion orcontraction of the cathode and yet prohibits any sideways movement ofthe rod.

In a particular embodiment tested an oxide cathode was used inconjunction with a thoriated tungsten heater coil. Support straps 13were of nickel to prevent workhardening of the material at the normaloperating temperatures. As an example of the expansion movementencountered in such an arrangement, the heater support assembly movedupward a distance of about .015 inch on each heating pulse.

Heating of the cathode is achieved by placing a high potential betweenbombarder heating coil 5 and the cathode 2. The plate power supply, bysuitable switching arrangements, may be used as the high potentialsource. In the test case emission temperature was reached in a period offrom 80 to milliseconds. Once the cathode is heated the plate supply maybe switched over to its normal function to accommodate an output demandpulse. Output demand pulses of 40 milliseconds duration are possiblebefore the cathode cools to below its emission temperature.

The instant invention, therefore, provides an electron tube cathodeassembly which eliminates the normal waste of heater power.

While the invention has been described by means of a specific exampleand in a specific embodiment, it is not limited thereto for obviousmodifications will occur to those skilled in the art without departingfrom the spirit and scope of the invention.

What is claimed is:

1. A cathode structure for use in an electron power tube capable ofbeing rapidly heated to emission temperature comprising;

a hollow conductive cylindrical cathode element having two open ends;

a conductive end plate covering one end of said cylindrical cathode andafiixed thereto;

a heater support rod extending through said cylindrical cathode alongits central longitudinal axis and rigidly attached at one of its ends tosaid end plate;

heater coils disposed about said heater support rod and supportedthereby;

a plurality of flexible bands radially and symmetrically disposed aboutthe other end of said heater support rod;

one end of each of said bands being rigidly attached to said other endof said heater support rod;

an insulated base member;

first means attached to said base for rigidly supporting the other endof said cylindrical cathode in a position above said base; and secondmeans attached to said base for rigidly supporting the other ends ofeach of said flexible bands in a position above said base.

2. The structure of claim 1 wherein said flexible bands are flat nickelstrips.

3. The structure of claim 1 wherein said plurality of bands are three innumber.

4. A cathode structure for use in an electron power tube capable ofbeing rapidly heated to emission temperature comprising;

a hollow conductive cylindrical cathode of low thermal mass and havingtwo open ends;

a conductive end plate covering one end of said cylindrical cathode andaflixed thereto;

a heater support rod extending through said cylindrical cathode alongits central longitudinal axis and rigidly attached at one of its ends tosaid end plate;

heater coil means connected to said heater support rod at a pointadjacent said end plate and disposed about the length of said heatersupport rod;

three flexible metal bands radially extending from the other end of saidheater support rod at right angles thereto and spaced from each other at120 intervals;

the ends of nearest said heater support rod of each of said flexiblebands being rigidly attached to said heater support rod;

an insulated base member;

a plurality of first support pins perpendicularly mounted on said baseand extending upwardly therefrom;

the upper ends of said first pins being rigidly attached to theremaining open end of said cylindrical cathode and adapted to supportsaid cathode in a position over said base and spaced therefrom; and

three second support pins mounted on said base extending upwardlytherefrom;

said second pins being disposed on said base so that their upper endsmate with the other ends of respective ones of said flexible bands;

each of said other ends of said flexible bands being rigidly attached tosaid upper ends of said second support pins.

5. The structure of claim 4 wherein said flexible bands are flat nickelstrips.

References Cited UNITED STATES PATENTS 2,082,120 6/1937 ROnci 313-2782,717,975 9/1955 Whitol 313331 3,038,098 6/1962 Neill 3l3250 FOREIGNPATENTS 1,286,724 1/1962 France.

JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner.

1. A CATHODE STRUCTURE FOR USE IN AN ELECTRON POWER TUBE CAPABLE OFBEING RAPIDLY HEATED TO EMISSION TEMPERATURE COMPRISING; A HOLLOWCONDUCTIVE CYLINDRICAL CATHODE ELEMENT HAVING TWO OPEN ENDS; ACONDUCTIVE END PLATE COVERING ONE END OF SAID CY LINDRICAL CATHODE ANDAFFIXED THERETO; A HEATER SUPPORT ROD EXTENDING THROUGH SAID CYLINDRICALCATHODE ALONG ITS CENTRAL LONGITUDINAL AXIS AND RIGIDLY ATTACHED AT ONEOF ITS END TO SAID END PLATE; HEATER COILS DISPOSED ABOUT SAID HEATERSUPPORT ROD AND SUPPORTED THEREBY; A PLURALITY OF FLEXIBLE BANDSRADIALLY AND SYMMETRICALLY DISPOSED ABOUT THE OTHER END OF SAID HEATERSUPPORT ROD; ONE END OF EACH OF SAID BAND BEING RIGIDLY ATTACHED TO SAIDOTHER END OF SAID HEATER SUPPORT ROD; AN INSULATED BASE MEMBER; FIRSTMEANS ATTACHED TO SAID BASE FOR RIGIDLY SUPPORTING THE OTHER END OF SAIDCYLINDRICAL CATHODE IN A POSITION ABOVE SAID BASE; AND SECOND MEANSATTACHED TO SAID BASE FOR RIGIDLY SUPPORTING THE OTHER ENDS OF EACH OFSAID FLEXIBLE BANDS IN A POSITION ABOVE SAID BASE.